Complex regulation of transforming growth factor beta 1, beta 2, and beta 3 mRNA expression in mouse fibroblasts and keratinocytes by transforming growth factors beta 1 and beta 2.

Abstract

Regulation of transforming growth factor Il1 (TGFII1), TGF(2, and TGF0i3 mRNAs in murine fibroblasts and keratinocytes by TGFIII and TGFI2 was studied. In quiescent AKR-2B fibroblasts, in which TGFOi induces delayed stimulation of DNA synthesis, TGFII1 autoregulation of TGFI1 expression was observed as early as 1 h, with maximal induction (25-fold) after 6 to 12 h. Increased expression of TGF(II mRNA was accompanied by increased TGFO protein production into conditioned medium of AKR-2B cells. Neither TGFI32 nor TGFI3 mRNA, however, was significantly induced, but both were apparently down regulated at later times by TGFI31. Protein synthesis was not required for autoinduction of TGFfII mRNA in AKR-2B cells. Nuclear run-on analyses and dactinomycin experiments indicated that autoregulation of TGF(l expression is complex, involving both increased transcription and message stabilization. In contrast to TGF(11, TGFj32 treatment of quiescent AKR-2B cells increased expression of TGFI1, TGFI82, and TGF,3 mRNAs, but with different kinetics. Autoinduction of TGF,I2 mRNA occurred rapidly with maximal induction at 1 to 3 h, enhanced TGFI83 mRNA levels were observed after 3 h, and increased expression of TGFI1 occurred later, with maximal mRNA levels obtained after 12 to 24 h. Nuclear run-on analyses indicated that TGFI2 regulation of TGF,I2 and TGF,3 mRNA levels is transcriptional, while TGFP2 induction of TGFI{1 expression most likely involves both transcriptional and posttranscriptional controls. In BALB/MK mouse keratinocytes, minimal autoinduction of TGF(H occurred at only the 12-and 24-h time points and protein synthesis was required for this autoinduction. The results of this study provide an example in which TGFI1 and TGF,2 elicit different responses and demonstrate that expressions of TGFII1, TGF,I2, and TGFj13 are regulated differently. The physiological relevance of TGFIV1 autoinduction in the context of wound healing is discussed.

Transforming growth factor‐β and bone morphogenetic protein‐2 act by distinct mechanisms to promote chick limb cartilage differentiation in vitro

“…This sequential regulation of developmental processes by TGF-P isoforms has been suggested by other investigators (Lyons et al, 1990;Fitzpatrick et al, 1990;Gatherer et al, 1990). In addition, studies have found that in some systems TGF-ps do regulate each other (Bascom et al, 1989;Jakowlew et al, 1992;Lehnert and Ackhurst, 1988).…”

Epidermal differentiation: the bare essentials.

“…Mere elevation of TGF-/~ mRNA expression is therefore not automatically an indication that active TGF-/~s are being produced. An example of this is the production of latent TGF-~I by human keratinocytes cultured under serum-free conditions at neutral pH (Bascom et al, 1989 Because the effects of TGF-/~s on basal cell growth appear to be largely reversible, it has been assumed that TGF-~s alone are not sufficient to induce terminal differentiation, a process thought to be irreversible. In support of this notion were early in vitro studies, showing that the biochemical indicators of terminal differentiation were not induced upon treatment of keratinocytes cultured on plastic with TGF-/3s (Kopan et al, 1987;Bascom et al, 1989).…”

“…An example of this is the production of latent TGF-~I by human keratinocytes cultured under serum-free conditions at neutral pH (Bascom et al, 1989 Because the effects of TGF-/~s on basal cell growth appear to be largely reversible, it has been assumed that TGF-~s alone are not sufficient to induce terminal differentiation, a process thought to be irreversible. In support of this notion were early in vitro studies, showing that the biochemical indicators of terminal differentiation were not induced upon treatment of keratinocytes cultured on plastic with TGF-/3s (Kopan et al, 1987;Bascom et al, 1989). More recent studies with differentiating culture systems have revealed that at greatly elevated levels, TGF-/3s can influence biochemical markers of keratinization, but at these high levels, they inhibit rather than promote, K1, K10, and filaggrin expression (Ma~nsbridge and Hanawalt,..1988;Choi and Fuchs, 1990).…”

“…sally in early embryos and localized later in the imaginal disks, which will form much of the adult epidermis of the fly (Padgett et al, 1987). In adult mammalian epidermis both in vivo (Thompson et al, 1989) and in vitro (Shipley et al, 1986;Van Obberghen-Schilling et al, 1988;Glick et al, 1989Glick et al, , 1990Bascom et al, 1989;Pelton et al, 1989), TGF-B1 and TGF-/T2 mRNAs are low, but detectable in the differentiating layers. In adult epidermis, TGF-/~ mRNAs can be upregulated (a) in an autoregulatory fashion (Van Obberg, hen-Schilling et al, 1988;Bascom et al, 1989), and (b) when mouse skin is treated with tumor-promoting agent (TPA) (Akhurst et al, 1988) or calcium (Glick et al, 1990), agents known to induce epidermal keratinization.…”

“…While epidermal chalones (see, for example, Richter et al, 1990) will undoubtedly receive more attention in the future, the most extensively studied negative regulators are the TGF-/3s, which act at picomolar concentrations to inhibit DNA synthesis and cell division (Shipley et al, 1986;Kopan et al, 1987;Bascom et al, 1989). The effect of TGF-/3s on growth is reversible, at least within a 48-h frame, and is not accompanied by gross changes in protein or RNA synthesis (Bascom et al, 1989). While TGF-/~s inhibit growth of basal cells, their natural expression in epidermis seems to be predominantly in suprabasal, differentiating layers.…”